The Cores will serve several functions, including 1) centralized neurological and neuropsychological instrument assessment and development directed at improving the methods for evaluating the AIDS dementia complex for both clinical and epidemiological studies; 2) a virology core facility for HIV isolation from CSF and blood specimens obtained in the various clinical studies, 3) an immunological studies core to assess immune cell profiles and immune function in the various clinical studies, and 4) a data acquisition and analysis core to organize and maintain a centralized database system and for centralized biostatistical analysis.